BELCHERTOWN - Sonja Farak, 35, of Northampton, a chemist at the Massachusetts State Crime Laboratory in Amhest, today denied charges of tampering with evidence and drug possession.

Farak was ordered held on $5,000 cash bail. She was arraigned in Eastern Hampshire District Court where she pleaded not guilty to two counts of tampering with evidence, one count of possession of a class A substance (heroin) and one count of possession of a class B substance (cocaine).

Farak was arrested at her home in Northampton on Saturday night after state police detectives assigned to the Northwestern District Attorney's office responded to a report of alleged evidence tampering made by authorities at the lab in Amherst where drugs seized by police in western and central Massachusetts are stored and analyzed. The case was then turned over to the Massachusetts attorney general's office.

Attorney General Martha Coakley on Sunday said that in one instance Farak allegedly removed a substance that had previously tested positive for cocaine and replaced it with a counterfeit substance that no longer tested positive. Investigators also allege that Farak possessed substances that appeared to be cocaine and heroin.

Farak is the second chemist charged in recent months with criminal activity in the state's drug analysis labs. Annie Dookhan, also 35, of Franklin, had worked at the state lab in Jamaica Plain and was accused last year of faking test results. That has thrown thousands of criminal cases into question.

"We allege that this chemist (Fartak) tampered with evidence, placing the integrity of that evidence in question," Coakley said Sunday. "Unlike our allegations against Annie Dookhan, this did not involve dry labbing or falsification of tests. On its face, the allegations against this chemist do not implicate the reliability of testing done or fairness to defendants."

Farak's lawyer, Elaine Pourinski of Northampton, said during the arraignment, "If we didn't have a case in the eastern part of the state, we wouldn't have such scrutiny in this case."